1. Field of the Invention
The present invention relates to an in-vehicle camera posture detecting apparatus and method for detecting an installation angle and the like of a camera that is mounted on a vehicle and captures an image of surroundings of the vehicle.
2. Description of the Related Art
In order to accurately detect the position or size of a subject included in an image captured by a camera mounted on a vehicle on the basis of the image, or in order to combine images of adjacent regions captured by cameras such that the resultant image is seamless, the installation position and angle of the camera or each camera have to be accurately determined.
The installation position and angle of a typical camera are often predetermined upon design of a system including the camera. Since an installation error is actually caused, calibration is performed after installation and the installation position and angle are then detected. For example, a camera installation angle calculating method has been known by which the installation position and angle of a camera are detected on the basis of images of a calibration sheet captured through the camera, the calibration sheet being placed in a predetermined position near a vehicle and having a printed calibration pattern including a plurality of calibration marks (refer to Japanese Unexamined Patent Application Publication No. 2010-183265 (pp. 2-11, FIGS. 1 to 23), for example).
The above-described method assumes that the calibration sheet is accurately placed in the predetermined position. Disadvantageously, if the placed calibration sheet is deviated from the predetermined position, the posture (position and angle) of the camera will fail to be accurately detected. For example, it is assumed that the calibration sheet is placed on the ground at the rear of the vehicle such that the placed calibration sheet is aligned with one end of a rear bumper and an image of the calibration sheet is captured by the camera installed in the rear of the vehicle. Although the position of the calibration sheet is positioned in that manner, it is difficult to align the calibration sheet with the end of the rear bumper, since the rear bumper is spaced apart from the ground. The same applies to the positions of the right and left sides of the calibration sheet. It is also difficult to accurately align the middle of the vehicle along the width thereof with the middle of the calibration sheet in the direction along the width of the vehicle.